var slideIndex = 0;
showSlides();

function plusSlides(n) {
  showSlides(slideIndex += n);
}

function currentSlide(n) {
  showSlides(slideIndex = n);
}

function showSlides(n) {
    var i;
    var slides = document.getElementsByClassName("mySlides");
    var dots = document.getElementsByClassName("dot");
    if (n > slides.length) {slideIndex = 1} 
  	if (n < 1) {slideIndex = slides.length}
    for (i = 0; i < slides.length; i++) {
        slides[i].style.display = "none"; 
    }
    for (i = 0; i < dots.length; i++) {
      dots[i].className = dots[i].className.replace(" active", "");
  	}
    slideIndex++;
    if (slideIndex> slides.length) {slideIndex = 1} 
    slides[slideIndex-1].style.display = "block"; 
    setTimeout(showSlides, 4000); // 间隔两秒后修改图片
    dots[slideIndex-1].className += " active";
}